OK, so this is a rather random/unusual question, but any info or
advice will be gratefully received. I've often played content from my
iPhone 5S into another source (digital recorder, amp, etc) for the
purposes of recording or for musical accompaniment. This has never
caused me any issues and, although VoiceOver leads to a small amount
of background hiss/static being expressed while the phone is talking,
the playback quality of audio material is unaffected by this and all
distortion/hiss stops as soon as the phone's speech output ends. I
therefore assumed that all iOS and iOSPad products would allow me to
do the same things, but I've found over the last few days (the first
time that I've actually tried to use other devices) that both the iPad
Mini and the iPod Touch (6th generation) present material with a much
greater amount of feedback once VoiceOver is activated, even if VO is
then turned off and no other gestures are used. These issues aren't
apparent when using the devices by themselves, but the additional
noises are very obvious to me when listening with headphones or
playing back a recording.

So, does anyone please know why my iPhone is much more obliging (for
example, because it uses more/less power than the other devices,
because it has a different type of speaker, because it draws on phone
signals, etc)? Also, presuming that my analysis so far is correct and
the iPhone is the way to go, would this be the same with larger/more
powerful/more recent models or only with older models like the 5S?

Many, many thanks in advance for any help.

Take care, Danny